Semiconductor transistors, in particular field-effect controlled switching devices such as a MISFET (Metal Insulator Semiconductor Field Effect Transistor), in the following also referred to as MOSFET (Metal Oxide Semiconductor Field Effect Transistor) and a HEMT (high-electron-mobility Field Effect Transistor) also known as heterostructure FET (HFET) and modulation-doped FET (MODFET) are used in a variety of applications. An HEMT is a transistor with a junction between two materials having different band gaps, such as GaN and AlGaN. HEMTs are viewed as an attractive candidate for power transistor applications, i.e., applications in which switching of substantially large voltages and/or currents is required. HEMTs offer high conduction and low resistive losses in comparison to conventional silicon based devices. HEMTs are typically formed from III-V semiconductor materials, such as GaN, GaAs, InGaN, AlGaN, etc.
Modern HEMT fabrication techniques require methods for etching type III-V semiconductor materials, such as GaN, GaAs, InGaN, AlGaN, etc. For example, many HEMT devices utilize a recessed gate configuration in which the gate structure is disposed in a recess that is formed in the barrier region of the device. This structure is typically formed by epitaxially growing the type III-V semiconductor layers and etching (either selectively or unselectively) material away from the barrier region to form the recess. Etching of type III-V semiconductor materials is commonly done using plasma and dry etching techniques due to the inertness of the material.
One issue with the etching of type III-V semiconductor materials relates to surface damage. For example, plasma etching of type III-V semiconductor materials can result in highly roughened surfaces with substantially dislocated crystalline material. In addition or in the alternative, plasma etching of type III-V semiconductor materials can create surface structures, e.g., needles or droplets. This surface damage creates an increased number of surface atoms along the etched surface. These surface atoms can serve as electrical traps by reconfiguring their atomic structure and electric charge state during electrical operation.